Nearly all modern alphabets are descended from an alphabet
invented 4000 years ago, probably by a group of people related to the
ancient
Hebrews, Phoenicians, and Canaanites, living in what is now the Sinai
desert.
They got the idea from the Egyptians, but used their own
simplified
pictures to represented consonant sounds. The Phoenicians and
others
of the region simplified the pictures further and often rotated them,
but
if you use your imagination, you can still make out where most of the
22
letters came from. If you turn the A with the point down, for
example,
you can see a representation of an ox head.

All the letters were for consonants, which is reasonable for Semitic
languages
like Phoenician, Hebrew, Arabic, and even Egyptian. Even aleph and
ayin actually represent the glottal sounds that preceded the A's.
Greek
(and most other languages) desperately need to represent vowels as
well,
so they took a few of the consonants they didn't need, and turned them
into
vowels -- aleph being the obvious example. They then added a few
symbols
of their own to represent extra sounds they needed. Three unused
letters
were retained in the Greek numbering system.

The Phoenicians, like the Hebrews and Arabs today, wrote from right to
left.
The Greeks originally did the same, then changed to a system
where
they changed direction every line, and finally to the present system of
left
to right. This has passed down to all the modern European alphabets.

The Latin alphabet, ancestor of most western European alphabets, is
derived
from the Greek, but was also influenced by the nearby Etruscan version
of
the alphabet. Over the centuries, extra letters were invented by
varying
older ones, or reintroducing Greek letters such as K and Y. It
wasn't
until the middle ages that small letters came into being, usually based
on
more cursive versions of the capital letters.

The alphabets of south and southeast Asia are all derived from the
Brahmi alphabet, which in turn is loosely based on the Aramaic.
With a far greater number of consonants, the ancient Indians created
many of their letters, and organized them phonetically. The
creativity continued as the idea moved eastward, and many of the later
alphabets bear little resemblance to the earlier ones (see below).

Also very creative are the Armenian and Georgian alphabets, presumably
based on Greek and Aramaic.

The
only
independently invented "true" alphabet is the beautiful Korean
hangul. There are also a number of syllabaries (where each symbol
represents a syllable rather than a single phoneme) that were
independently invented, including two for Japanese, one for Cherokee,
and one for the Cree and Inuit of Canada.

Examples of the variety of Brahmi-derived
scripts of south and southeast Asia: